This invention relates primarily to prosthetic devices such as ventilation or drain tubes which are surgically inserted in the ear drum and are useful for equalizing pressure between the middle and outer ears and draining otitus media from the middle ear. More particularly, the invention relates to a one-way valve for inclusion in a ventilation tube which permits liquid, e.g. otitus media, to drain from the middle ear to the outer ear while at the same time preventing liquid from passing from the outer ear to the middle ear and permitting gaseous communication between the middle and outer ears when the valve is open for equalizing pressure between them.
By way of background, the typical remedy for middle ear effusion is a myringotomy, which is a surgical procedure that involves cutting a slit in the eardrum to alleviate a build-up or reduction of pressure in the middle ear cavity. A variety of ear ventilation tubes for insertion into such a slit have been introduced over the years. The tube primarily keeps the ear drum slit open for a sufficient period of time following the surgery to allow pressure to equalize between the middle and the outer ears. Frequently the condition of buildup or reduction of pressure in the middle ear cavity which the tube is intended to alleviate requires that the tube remain in place for a significant period of time.
One problem associated with the use of such ventilation tubes is that they may permit the ingress of potentially contaminating fluids such as water from bathing or swimming, which may aggravate the condition which the tube was intended to alleviate. For this reason, patients fitted with such ventilation tubes have been instructed to take special precautions, for example, using cotton or a wax plug to block the exterior tube opening when bathing, and ordinarily have been advised not to swim.
There are prior art ventilation tubes which have been designed to prevent liquid from entering the middle ear cavity so that the wearer is not unduly restricted in his or her activities. For example, U.S. Pat. No. 4,326,512 to Peerless teaches a ventilation tube device which includes a piston or plug for temporary insertion in the tube to permit the patient to participate in normal activities, including swimming. Although providing a partial solution to the problem, a patient-inserted device has disadvantages. For example, in the process of inserting or removing the plug, the patient may dislodge the ventilation tube, risking damage to the ear and/or requiring reinsertion of the tube. In addition, the piston or plug may cause contamination problems and aggravate the infection. Although have a physician insert the plug may minimize these risks, this would be costly and inconvenient. Furthermore, such pistons or plugs do not permit passage of fluids or gases from the middle ear to the outer while inserted, substantially preventing the ventilation tube from performing its pressure equalization and drainage functions until the plug is manually removed.
It has also been proposed to use a gas permeable-liquid impermeable covering for the exterior opening of an ear ventilation tube to prevent ingress of fluids to the middle ear, but at the same time allow pressure equalization. Examples of such membranes can be found in U.S. Pat. Nos. 3,916,873 to Wasserman, 4,094,303 to Johnston, and 4,169,697 to Cantekin. Although tubes including such membranes are acceptable for equalizing gaseous pressure between the middle and outer ear, these membranes do not permit fluid drainage from the middle to outer ear. For this reason, they are not suitable for applications where the wearer's condition includes fluid build-up in the middle ear or the potential for such build-up. Not only would they not permit drainage, but should fluid build-up occur, the fluid pressure may cause expulsion of the ventilation tube requiring surgical reinsertion.
Although various types of valves have been used in devices implanted in the human body, they all relate to controlling the flow of liquids and require significant fluid pressure to control the valve. None is known which is designed to allow two-way gaseous communication when the valve is open and restrict liquid flow to one direction, and is designed to operate with minimal fluid pressure. Such liquid valves are taught in U.S. Pat. Nos. 3,926,215 to Macleod and 4,319,364 to Kaster where generally pivotally mounted two-way disc valves permit free fluid flow in one direction and restrict, without completely blocking, fluid flow in the opposite direction. U.S. Pat. No. 3,997,923 to Possis describes a two-way ball-type valve also for restricting fluid flow in one direction, and is primarily directed toward a permanent housing for the valve which permits replacement of the valve mechanism without removing its associated housing. U.S. Pat. No. 3,768,102 to Kwan-Gett, et al. teaches an artificial urethral valve including a ball and spring arrangement which requires a relatively high breakaway or opening force to open the valve, and thereafter a constant outflow of fluid to maintain the valve in its open position. These types of valves are not suitable for applications where significant fluid pressure is not available on both sides of the valve or where a valve is designed to remain open unless liquid pressure on one side forces it to close.